In cleaning and antimicrobial operations, commercial users (e.g., restaurants, hotels, food and beverage plants, grocery stores, etc.) rely upon the concentration of a cleaning or antimicrobial product to make the product work effectively. Failure of a cleaning or antimicrobial product to work effectively (for example due to concentration issues) can cause a commercial user to perceive the product as lower quality. End consumers may also perceive the commercial provider of such products as providing inferior services. In addition, commercial users may be investigated and/or sanctioned by government regulatory and health agencies. Accordingly, there is a need for a system that can monitor the characteristics of fluid solutions, e.g., to determine if the concentration of a product is within a specified concentration range. The same may be true for other applications, such as commercial and industrial water treatment, pest control, beverage and bottling operations, oil and gas refining and processing operations, and the like.
One method of monitoring the concentration of a product relies on electroanalytical methods to measure various parameters of the product. One such parameter can be the conductivity of the product. Some existing conductivity sensors comprise two electrodes, and operate by applying a voltage across the two electrodes and measuring a resulting current. The relationship between the magnitudes of the current and the voltage allow the resistance and therefore conductivity of the product to be determined. Such two-electrode designs can result in fouling effects at the electrodes and/or narrow ranges of operation.
More expensive four-electrode devices have been used to overcome some of the shortcomings of the two-electrode designs. Exemplary four-electrode devices can pass a current from one electrode to another to maintain a certain voltage between two separate electrodes. Other devices pass a known current between two of the electrodes and measure the voltage difference between the other two electrodes. One disadvantage of such designs, however, is that in some cases, such as in the case of high product resistance, the device must apply an undesirably high voltage in order to achieve an appropriate current. High voltages can cause electrode polarization, unwanted electrochemical reactions within the sample, and fouling of the electrodes.